ISPN-3308 Change the tests' JGroups rejection policy to Discard

Includes some smaller changes to make the test configuration more like the
production configuration.
the jdk6testsuite is not activated by a system property now.
ISPN-3289 PutForExternalRead should only write the value on the originator once

Use the same condition to decide whether a PFER should write to the data
container as for a non-tx put, even in tx caches.